Polyphenylene ether resins are known as high performance engineering thermoplastics possessing high melt viscosities and softening points which makes them useful for many applications where resistance to high temperatures is desired, and it is well known that properties of the polyphenylene ether resins can be altered materially by blending with other resin materials.
As described in U.S. Pat. No. 4,972,021, blends of polyphenylene ethers and polyolefins are of great interest because they can bring some of the chemical resistance of the polyolefins to the polyphenylene ether. Specific blends of polyphenylene ether resins and polypropylene resin are disclosed therein. Other non-foamed blends or combinations of polyolefin resins with polyphenylene ether resins are described in U.S. Pat. Nos. 4,383,082, 4,584,334 and 4,764,559.
It is known in the prior art to form foams from blends of polyphenylene ether resin and polystyrene resin or high impact polystyrene, i.e., rubber-modified grafted polystyrene, imbibed with volatile blowing agent such as chlorinated hydrocarbons, which ultimately result in pre-expanded particles of the polyphenylene ether resin and polystyrene. For example, in U.S. Pat. No. 4,782,098, a shaped polymer foam structure is obtained by imbibing particles of an interpolymer of a polyphenylene ether resin and a polymerized vinyl aromatic monomer under pressure with an easily volatilizable hydrocarbon or halogenated hydrocarbon blowing agent; heating the imbibed particles to a temperature sufficient to cause expansion of said particles to a density significantly less than that of the imbibed particles; and filling a mold with the expanded particles and subjecting the particles to sufficient heat to fuse the particles together on cooling to form a shaped coherent foam structure.
Foamed polyolefins are also known in the prior art. In U.S. Pat. No. 4,379,859, pre-foamed particles of polypropylene resin are produced by dispersing substantially non-crosslinked polypropylene resin particles composed of an ethylene/propylene random copolymer or a mixture of an ethylene/propylene random copolymer and low-density polyethylene and/or an ethylene/vinyl acetate copolymer as a base resin and a volatile blowing agent in water in the presence of a dispersing agent within a closed vessel; heating them to a temperature above a point at which the particles soften, thereby to impregnate the blowing agent in the particles; and while maintaining the pressure of the inside of the vessel higher than the vapor pressure of the blowing agent, opening one end of the vessel to release the particles and water simultaneously into an atmosphere kept at a lower pressure than the inside of the vessel. Other pre-foamed particles of polyolefin resins and the method of their manufacture are described in U.S. Pat. Nos. 4,399,087, 4,443,393, 4,504,601 and 4,720,509.
For certain applications, it is desirable to form foamed resin articles from the blends of polyphenylene ether resins and polyolefin resins in order to obtain foamed articles having the improved properties found in the non-foamed prior art articles. For instance, it would be desirable to provide foamed automotive parts, for example, automobile bumpers, having the combined properties of polyphenylene ether resin and polyolefin resins. Although expandable, pre-expanded and foamed polyolefin resins or blends of polyphenylene ether resin and polystyrene resins are well-known in the art as described above, the known art does not provide expandable, pre-expanded and foamed resins of polyphenylene ether resin combined with polyolefin resins or a method of making them.